The present invention relates to a display device, and more particularly, to a transflective liquid crystal display device.
Liquid crystal display (LCD) devices are widely used in electronic devices such as portable computers, PDAs and cell phones. LCD devices can be classified into transmissive and reflective types. A transmissive LCD utilizes a backlight as light source, while a reflective LCD utilizes ambient light. Since a transmissive LCD uses a backlight, it can appear brighter and can be used in environments with low ambient light. However, the backlight for a transmissive LCD consumes power and makes the device larger. In contrast, a reflective LCD relies on ambient light, and thus, it has the advantage of lower power consumption. Unfortunately, a reflective LCD device is difficult to shoe image in environments with low ambient light.
In order to overcome the drawbacks of these two types of LCDs, transflective LCDs have been developed. A transflective LCD is capable of displaying images in both transmissive and reflective modes. In bright ambient light, the backlight of a transflective LCD can be deactivated, thus lowering its power consumption. When less ambient light is available, the backlight of the transflective LCD is activated, thus improving its image quality over that of the reflective LCD.
FIG. 1 shows an exploded perspective view of a conventional transflective LCD device comprising an upper substrate 10 and a lower substrate 20. A liquid crystal layer 50 is interposed between upper substrate 10 and lower substrate 20. Upper substrate 10 is a color filter substrate. Lower substrate 20 is an array substrate.
In upper substrate 10 on the surface opposing lower substrate 20, a black matrix 12 and a color filter layer 14 including a plurality of red (R), green (G), and blue (B) color filters are formed. Black matrix 12 surrounds each color filter in an array matrix. A common electrode 16 is then formed to cover color filter layer 14 and black matrix 12.
In lower substrate 20 on the surface opposing upper substrate 20, a thin film transistor (TFT) serves as a switching device and is formed in an array matrix corresponding to color filter layer 14. In addition, a plurality of crossing gate lines 26 and data lines 28 are positioned such that each TFT is located near each cross point of the gate and data lines 26 and 28. In addition, a plurality of pixel regions (P) are defined by the gate and data lines 26 and 28. Each pixel region P has a pixel electrode 22 comprising a transparent portion 22a and an opaque portion 22b. Transparent portion 22a comprises a transparent conductive material, such as Indium Tin Oxide (ITO) or Indium Zinc Oxide (IZO). Opaque portion 22b comprises a metal having superior reflectivity, such as Al (aluminum).
FIG. 2 shows a sectional view of a conventional transflective LCD device comprising a lower substrate 200 and an upper substrate 260. A liquid crystal layer 230 is interposed between lower substrate 200 and upper substrate 260.
Lower substrate 200 has an insulating layer 210 and a pixel electrode 220 formed thereon. Pixel electrode 220 has an opaque portion 222 and a transparent portion 224. Opaque portion 222 can be an aluminum layer, and transparent portion 224 can be an ITO layer. Opaque portion 222 reflects ambient light 270, while transparent portion 224 passes light 280 from a backlight device 290 at the rear of lower substrate 200. On the exterior of lower substrate 200, a lower compensation film 291 and a lower polarizer 292 are also formed.
Backlight device 290 is arranged below lower polarizer 292. Backlight 290 typically comprises numerous fluorescent tubes arranged parallel to a light guide plane, with a back reflector enhancing brightness, and a diffuser layer on the light guide plane providing more uniform illumination to the liquid crystal device. For example, in portable displays, small diameter cold cathode fluorescent tubes are situated at one end or opposing ends of a light guide panel which directs light toward the LCD panel. Conventional backlight modules with fluorescent lamp sources are, however, thicker and limit scaling.
Upper substrate 260 has a common electrode 240 and a color filter 250 formed thereon. Color filter 250 includes red (R), green (G), and blue (B) regions. On the exterior of upper substrate 260, an upper compensation film 293 and an upper polarizer 294 are formed.
As noted, liquid crystal layer 230 is interposed between lower substrate 200 and upper substrate 260. The transflective LCD device is thus capable of operating in both reflective and transmissive modes. For example, during transmissive operation, light 280 is generated from backlight 290 penetrates transmissive portion 224 and passes through color filter 250. Ambient light 270 can also be reflected by reflective portion 222 and passes through color filter 250 again.
Unfortunately, a conventional transflective LCD still requires a backlight device or the like below the LCD panel, which increases its volume, weight and fabrication costs. Additionally, in conventional LCD devices, polarizers are fixed to the outside surfaces of the LCD panel. Gaps may thus exist between the polarizers and the LCD panel, allowing light leakage, and decreasing light utilization efficiency of the LCD device.